The biological clock also ticks for fathers

Wednesday 2 November 2005 20.38 EST
First published on Wednesday 2 November 2005 20.38 EST

The biological clock ticks for men as well as women, suggesting it is not just females who should be aware of the consequences of starting families later in life, according to research published today.

In the biggest ever study into the effects of paternal age on babies' health, scientists found that older men have a greater chance of fathering children with Down's syndrome and are more likely to have babies with a variety of limb defects.

Previous studies have found that sperm, as well as eggs, accumulate genetic mutations as they age, which can lead to a drop in male fertility. But the effect of such genetic damage on children born to older fathers has proved hard to pin down.

In the latest study, epidemiologist Jorn Olsen, at the University of California, Los Angeles, used the Danish Fertility Database, which holds information on 70,000 couples and their firstborn child, to look for differences in children with older fathers. Men aged 50 and above were more than four times more likely to have a child with Down's syndrome. Children with limb defects were also more common. The study appears in the journal Human Reproduction.

The finding caused concern yesterday among some fertility specialists, who have seen the age of sperm donors increase with the government's abolition of sperm donor anonymity earlier this year. "With the change in the law, donors tend to be men who have already had their families," said Allan Pacey, a fertility expert at Sheffield University.

"But about a third of all births in the UK are from men who are older than 35 and, frankly, that's not the best sperm to use in fertility treatment. You want sperm from young, healthy guys that hasn't had time to build up defects."

Age has a big impact on the fertility of women and the health of their babies. Female fertility drops steeply above the age of 35 and the risk of miscarriage increases: at the age of 40 and above, 40% of pregnancies will be miscarried.

Figures from the US National Institutes of Health show that the chances of having a baby with Down's syndrome increase rapidly with a woman's age. About one in 1,000 babies born to mothers under 30 have Down's syndrome, a figure that becomes one in 400 by the age of 35 and one in 105 by the age of 40.

While the medical risks of starting families older are smaller for older fathers than for women approaching the menopause, the trend of couples starting families later in life means the issue of male age should be taken into consideration, Dr Olsen told New Scientist magazine. In 2002, scientists at the University of Washington reported a study of sperm quality in 60 men aged 22 to 60. They found that men aged 35 and above had more sperm with broken strands of DNA and that the sperm were less active, suggesting their chances of successfully fertilising an egg were lower.